#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <assert.h>

struct s_string {
    unsigned int count;
//    char *data; //不能用这种方式
    char data[0];
};
typedef struct s_string String;

char *fold(String *);

void copy(void *, const void *, unsigned int);

unsigned int length(const char *);

String *init(const char *);

String *concat(String *, const char *);
